1. Field of the Invention
This invention relates to a method for the production of a breathable multilayer synthetic leather with a backing layer of a textile sheet, at least one intermediate layer based on an at least partially open-cell whipped polyurethane foam that is applied to the backing layer, and an outer layer based on a polyurethane that is applied to the entire surface of the at least one intermediate layer, where, in a first step, the outer layer is applied to the entire surface of a detachable underlay and hardened, the at least one intermediate layer is applied to the outer layer, then the backing layer is laid onto the at least one intermediate layer, and the underlay is detached from the outer layer.
2. Discussion of Related Art
Methods for the production of synthetic leathers are known, for example, from German Patent Reference DD 259 106 A3 and are distinguished by the fact that the layers are produced using the so-called reverse process, wherein, first the subsequent visible surface, such as the top surface of the outer layer, is formed on the supporting surface of the underlay and then the remaining layers are applied until finally, the backing layer is applied, which will later form the underside of the finished synthetic leather. After the entire layer structure has been formed, the underlay is detached from the outer layer so that the visible side is accessible, the finished synthetic leather is turned over and the outer layer can then be provided with an embossing or other additional surface treatment.
Breathable multilayer synthetic leathers are particularly suitable for use in automotive interiors, for example as seat covering material, because the breathable property assures greater seat comfort and prevents perspiration on a vehicle seat covered with the material.
While the textile sheet backing layers and the whipped polyurethane foams used for the intermediate layers are inherently accompanied by a certain open-porosity that is necessary for achieving the breathability, it has been difficult to produce a porous, full-surface polyurethane-based outer layer because the polyurethane dispersions that are applied to an underlay in the reverse process usually tend, as they harden, to form a closed film that lacks the very pores desired, making it necessary to produce pores in the outer layer in an additional work step, such as with needle perforation or stretching. But this is not only laborious, it also influences the visual appearance of the outer layer because the pores produced by needle perforation are easily visible to the naked eye.
European Patent Reference EP 1 279 762 discloses the production of a breathable synthetic leather of the type mentioned above, but the film formation in the outer layer prevents a porosity required for the breathability. If the known synthetic leather is to have a porous and therefore breathable outer layer, then the outer layer is not applied to the entire surface, but is instead introduced into recesses of an underlay structured like leather so that openings are produced between the outer layer regions formed in the recesses. A synthetic leather of this kind has many disadvantages, for example a low abrasion resistance of the outer layer.
PCT International Publication WO 2005/047549 discloses an application of a finishing layer of an aqueous plastic dispersion onto a structured underlay heated to a temperature below 105° C. in order to form a film after the evaporation of the water. The layer thus produced has some pores, but the breathability, particularly with regard to the number and size of the pores, allows for improvement due to the film formation.